This invention is directed to certain silicone organic blends having an unexpected improvement in their viscosity stability, rendering them especially useful as lubricating oils, hydraulic fluids, dielectric fluids, and as coolants or heat transfer media.
Different fluids have different rates of change in viscosity with temperature. The Viscosity Index (VI) is a method for applying a numerical value to this rate of change based on a comparison with the relative rates of change of two arbitrarily selected types of oils that differ widely in this characteristic. A high VI indicates a relatively low rate of change of viscosity with temperature. A low VI indicates a relatively high rate of change of viscosity with temperature. A standard method for calculating the Viscosity Index is described in ASTM D2270.
One of the primary performance features of any fluid for use as a lubricant, hydraulic fluid, dielectric, or coolant, is that it have outstanding flow characteristics at low temperatures and stability at high temperatures, i.e., a high VI.
Silicones have high Viscosity Indexes, some VI""s being about 300 or more. For comparison, cycloparaffinic lubricating oils have a VI of 15, while paraffinic lubricating oils have a VI of 100.
In any event, and in spite of the high VI possessed by some silicones, there remains a need for improvement in viscosity stability of silicones and silicone organic blends in many applications as lubricants, hydraulic fluids, dielectrics, or coolants.
The improved viscosity stability of our silicone organic blends enhance their value in general industrial lubricant applications including, for example, their use as hydraulic oils, gear oils, turbine-circulation oils, refrigeration oils, compressor oils, vacuum pump oils, brake fluids, and damping media. In electrical devices, these silicone organic blends are useful as dielectric fluids in convective or forced circulation type capacitors and transformers. They are also useful dielectric fluids in other electrical devices such as electrical cable, rectifiers, electromagnets, switches, fuses, circuit breakers, and as coolants and insulators for dielectric devices such as transmitters and receivers.
In specialty applications, they can function as multi-purpose fluids, as in electrically driven compressors or vacuum pumps of the type described in U.S. Pat. No. 5,222,874 (Jun. 29, 1993), where an oil is used to lubricate and cool the moving parts of a compressor, and is also used to cool the stator laminations and windings of the motor driving the compressor.